The invention relates to improvements in methods of patching up defective conduits for liquids, particularly to improvements in methods of patching up sewage pipes. Still more particularly, the invention relates to improvements in patching up of cracked and/or otherwise damaged pipes from within while the pipes are buried in soil or another material.
German Pat. No. 39 22 351 Al discloses a method of restoring the integrity of portions of buried pipes with a resin-impregnated single-layer mat of fibrous material. The mat is convoluted onto a radially expandible hose which is expanded from within to urge the mat against the internal surface of the defective portion of a pipe. The marginal portions of the mat which surrounds the expandible carrier overlap each other to thus ensure that the convoluted mat continues to remain a tubular body upon completion of the expanding operation. The arrangement is or should be such that the marginal portions of the mat overlap each other by an angle of approximately 90.degree. when the step of expanding the hose (and the surrounding mat) is completed.
The expandible hose for the convoluted mat remains at a standstill in the course of the expanding step, i.e., while the mat is being expanded radially outwardly toward and into engagement with the internal surface of a defective portion of a pipe. The overlapping marginal portions of the mat are in frictional engagement with and rub against each other while the hose and the convoluted mat thereon are subjected to radial expanding action by a pressurized fluid which is admitted into the hose. Furthermore, radial expansion of the hose entails a movement of the expanding mat relative to the hose. Therefore, the resin which permeates the convoluted mat does not issue at the periphery and/or beyond the axial ends of the expanding mat. At any rate, the quantity of resin which is expelled from the mat radially outwardly and/or axially is negligible and, therefore, the force with which the expanded mat adheres to the internal surface of the pipe is relatively small. Some radial compression of the single layer of resin-impregnated mat takes place only when the expanding step is completed and the expanded hose continues to exert pressure against the expanded mat, i.e., the single layer of the mat is caused to reduce its thickness and to be relieved of some resin only when the damaged portion of the pipe is called upon to act as an anvil or back support for the expanded mat.
A drawback of the aforedescribed prior proposal is that the damaged portion of the pipe (the damaged portion is likely to exhibit one or more cracks which permit the conveyed flowable material (such as raw sewage) to escape from the buried pipe and to penetrate into the soil around the pipe) must stand quite pronounced radially outwardly oriented stresses which are applied by the expanded tubular mat and are likely to cause additional damage, such as widening of the cracks or complete disintegration of the pipe into several discrete fragments. Moreover, the quantity of resin which is expelled from the tubular mat upon completion of the expanding step is relatively small so that the resin (if any) which is expelled from the mat cannot fill the cracks and cannot ensure reliable bonding of the expanded tubular mat to the adjacent internal surface of a damaged portion of the pipe.